# tau

a terminal-based AI chat client for working with code. tau gives you access to Claude, GPT, and Gemini models, each equipped with tools to explore, read, write, and edit files in your project, plus optional sub-agents for background tasks.

![tau](https://raw.githubusercontent.com/markusylisiurunen/tau/main/assets/tau.png)

## installation

```sh
npm install -g @markusylisiurunen/tau@latest
```

you'll need an API key from at least one provider. set it via environment variable:

```sh
export ANTHROPIC_API_KEY=sk-ant-...
# or OPENAI_API_KEY, or GEMINI_API_KEY, or PARALLEL_API_KEY, or MISTRAL_API_KEY (for /listen, Telegram audio, and tau tool pdf-unpack)
```

or store keys in `~/.config/tau/config.json`:

```json
{
  "apiKeys": {
    "anthropic": "sk-ant-...",
    "openai": "sk-...",
    "google": "...",
    "parallel": "...",
    "mistral": "..."
  }
}
```

for built-in providers and features, use these `apiKeys` entries: `anthropic`, `openai`, `google`, `parallel`, and `mistral`. tau checks the matching `apiKeys.<provider>` entry before environment variables.

`parallel` is only needed for `web_search`/`web_fetch` usage in sub-agents and can be provided through `apiKeys.parallel` or `PARALLEL_API_KEY` (`PARALLEL_API_KEY` takes precedence).

`/listen`, Telegram audio transcription, and `tau tool pdf-unpack` all use `apiKeys.mistral` or `MISTRAL_API_KEY` (`MISTRAL_API_KEY` takes precedence). `/listen` also requires `ffmpeg` on your system and is currently supported only on macOS. `tau tool pdf-unpack` also requires `pdftoppm` from Poppler on your system.

`/speak` uses the Google provider (`apiKeys.google` or `GEMINI_API_KEY`) and is currently supported only on macOS.

### OpenAI Codex subscription (ChatGPT Plus/Pro)

to use the OpenAI Codex subscription provider (`openai-codex`), run:

```sh
tau auth login codex
```

this prints a login URL and starts a local callback server on `127.0.0.1:1455`. complete the login in your browser and tau will store tokens in `~/.config/tau/auth.json`. if port `1455` is already in use, or the browser callback fails, tau will prompt you to paste the redirect URL/code. if you see token refresh errors later, run the login command again to re-authenticate.

to list authenticated accounts and usage:

```sh
tau auth list
```

to remove stored credentials:

```sh
tau auth logout codex --account <email>
```

to force a specific Codex account for this run, set `TAU_CODEX_ACCOUNT` to the account email or account id (same matching as `auth logout`). when set, tau will only use that account and will not fail over.

`openai-codex` does **not** use `OPENAI_API_KEY` or `apiKeys.openai`; it relies on the OAuth tokens in `~/.config/tau/auth.json`.

## usage logging

tau writes JSONL usage logs to `~/.config/tau/logs/usage-YYYY-MM-DD.jsonl` for every assistant response (main and sub-agent). summarize usage with:

```sh
tau usage --since 2025-01-01 --persona gpt-5.4-coder
```

filters: `--since`, `--persona`, `--provider`, `--model`.

## RPC mode (headless stdio)

tau can run without the TUI via NDJSON RPC over stdin/stdout:

```sh
tau rpc --persona gpt-5.4-coder --risk read-only
```

RPC mode reuses the same startup config, persona loading, and risk handling as interactive mode. stdin/stdout are reserved for protocol traffic in this mode (piped stdin is **not** treated as an initial user message). `--caffeinated` is a macOS-only TUI flag and is rejected in RPC mode.

for protocol details and examples, see [docs/rpc.md](docs/rpc.md).

## async daemon (HTTP + Telegram)

tau also supports an async daemon for queued/background sessions:

```sh
tau async daemon --config-file <path>
```

client command surface:

```sh
tau async --project <id> <prompt...>
tau async <prompt...>
tau async -- <prompt...>
tau async list
tau async status <id>
tau async logs <id>
tau async send <id> <text...>
tau async interrupt <id>
tau async cron list
tau async cron runs [jobId]
tau async cron run <jobId>
```

project id for `tau async <prompt...>` resolves from `--project <id>` first, then `async.client.defaultProjectId` from config.

use `tau async -- <prompt...>` when prompt text starts with a reserved command word (for example, `list`).

for daemon/API/Telegram details, see [docs/async.md](docs/async.md).

daemon config uses a bot-id map (`telegram.<botId>.botToken`), with optional per-bot `allowedProjectIds` scoping. Telegram sessions are chat-scoped per bot (no cross-chat or cross-bot session sharing).

Telegram DM input supports plain text, voice/audio transcription, and attachment queueing (`image/*`, PDF, `.txt`, `.md`, `.json`, `.csv`, `.yaml`, `.yml`). attachment-only messages do not trigger turns, attachments are downloaded to local temp files immediately, queued attachments are prepended to the next text/voice turn as local temp file metadata, and oversized Telegram replies are split into 95%-of-limit chunks sent 1 second apart.

daemon config also supports `systemMessage`, `cron.jobsDir`, and `cron.systemMessage` for scheduled runs, plus per-project `workingDirectory` (for monorepos), `description` (used by Telegram `/projects`), `bootstrapCommands` (blocking), and `backgroundBootstrapCommands` (non-blocking). on startup, the daemon wipes existing entries under configured async workspace roots. on Telegram adapter startup, tau also prunes stale `tau-telegram-attachments-*` directories under the system temp directory. Telegram `/close` deletes session workspaces from disk when closing sessions.

## built-in tool commands

tau also ships a small `tau tool` command family for utility workflows outside the chat UI.

```sh
tau tool pdf-unpack ./docs/spec.pdf
```

`tau tool pdf-unpack` sends the original PDF to Mistral for OCR/Markdown, renders page image patches locally with `pdftoppm`, writes a persistent temp directory with `document.md`, `pages/`, and `images/`, and prints the output paths as plain text for follow-up model use.

## SDK usage (Node)

tau also ships a Node SDK at `@markusylisiurunen/tau/sdk` that talks to the same RPC subprocess (`tau rpc`) behind the scenes.

```ts
import { createTauSdkClient } from "@markusylisiurunen/tau/sdk";

const client = await createTauSdkClient();
const unsubscribe = client.onEvent((event) => {
  // stream core events
});

try {
  const result = await client.submit("summarize this repo");
  console.log(result.userHistoryEntryId, result.turn.aborted);

  const snapshot = await client.snapshot();
  console.log(snapshot.sessionId, snapshot.historyLength);

  await client.shutdown();
} finally {
  unsubscribe();
  await client.close();
}
```

for full API details (options, methods, events, and errors), see [docs/sdk.md](docs/sdk.md).

## install starter prompts and skills

tau ships starter prompt and skill templates as markdown content in this repository, including guided-review templates for splitting changes into focused review chunks. install them with:

```sh
tau install
```

this writes prompts and skills into `.tau/` under your current working directory. use `--global` to install into `~/.config/tau/` instead, and `--force` to overwrite existing files/directories. use `--prompt <id>` or `--skill <name>` to install only one item (for targeted updates).

## security notice

**the risk level system is a UX guardrail, not a hard security boundary.** it helps prevent accidental writes and guides model behavior, but it has significant limitations:

- **model trust**: the bash tool relies on the model honestly declaring whether a command is a read or write. there's no runtime validation that the command actually matches the declared intent. a model could declare `safetyLevel="read"` while running `rm -rf /`.
- **no command analysis**: the system doesn't inspect command content. it trusts the declared safety level without verifying what the command actually does.
- **full system access**: the model can access any file on your system that your user account can read or write, not just the current working directory. if you need stronger isolation, run Tau inside a VM or container.
- **no tty / non-interactive tools**: tool commands run with stdin ignored and no TTY. anything that prompts for input or opens an editor can hang or fail (for example `sudo`, `ssh` password prompts, `git` credential prompts). tau also forces git into non-interactive mode (no prompt/editor/pager, batch-mode ssh).
- **user bypasses**: the `!` prefix executes shell commands directly and completely bypasses risk level checks. this is intentional for direct use, but means risk levels only constrain the model, not the user.

note that there is no confirmation step before tool execution. the model runs commands immediately, and you can only observe the results after the fact.

## getting started

tau requires Node.js 24.x and runs on macOS and Linux (Windows is unsupported).

for development from source:

```sh
npm install
(cd src/diff_tool/app && npm install)
npm run build
npm start
```

`npm start` launches the interactive TUI and expects a real terminal.

## themes

tau can load custom palette overrides from theme files. create a theme at:

- `.tau/themes/<id>.json` (project)
- `~/.config/tau/themes/<id>.json` (global)

then set `"defaultTheme": "<id>"` in config. any palette token not defined in the file renders as plain text. theme values accept `#rgb`, `#rrggbb`, `rgb(r, g, b)`, or `hsl(h, s%, l%)`. hex without `#` is ignored.

built-in themes are available by default with ids: `crimson`, `ember`, `gold`, `lime`, `grass`, `emerald`, `jade`, `teal`, `cyan`, `azure`, `cobalt`, `violet`, `purple`, `magenta`, `rose`. built-ins auto-adapt to dark/light terminal backgrounds via OSC 11 detection at startup (best effort, dark fallback). set `defaultTheme` to one of these ids, or disable them with `disableBuiltinThemes`.

custom themes loaded from `.tau/themes` or `~/.config/tau/themes` are single-variant and use exactly the tokens you define.

available palette tokens (theme keys):

- core: `brandAccent`, `textMuted`, `textDim`, `linkText`, `thinkingText`, `codeInlineText`, `codeBlockText`
- editor: `editorBorderNone`, `editorBorderMinimal`, `editorBorderLow`, `editorBorderMedium`, `editorBorderHigh`, `editorBorderXhigh`, `editorSubagentBorder`, `editorBorderRecording`
- status: `statusWarn`, `statusError`, `modeMemory`, `modeBash`
- action: `actionRunning`, `actionSuccess`, `actionError`, `actionOutput`
- diff: `diffAdd`, `diffRemove`
- toasts: `toastSuccess`, `toastWarn`, `toastError`
- user: `userSurface`, `userMemorySurface`, `userMemoryText`
- risk: `riskReadOnlyText`, `riskReadWriteText`

example theme file (`.tau/themes/solarized.json`):

```json
{
  "brandAccent": "#b58900",
  "textMuted": "#586e75",
  "textDim": "#657b83"
}
```

and in config (`.tau/config.json` or `~/.config/tau/config.json`):

```json
{ "defaultTheme": "solarized" }
```

## risk levels

tau uses risk levels to control what the model can do. this lets you stay in control while working alongside AI.

- **read-only** (default): model can run read-only tools (no file modifications)
- **read-write**: model can create, edit, and delete files

sub-agents inherit the session risk level unless overridden in persona config. a sub-agent configured with `riskLevel: read-write` can write even when the main session is `read-only`.

start with a specific risk level (exact values: `read-only` or `read-write`):

```sh
tau --risk read-write
```

or change it during a session with `/risk:read-only` or `/risk:read-write`.

the default is read-only because it lets the model investigate your code and answer questions without risk of unintended changes. bump it to read-write when you're ready to let the model make edits.

## power management (macOS)

start tau with `--caffeinated` to keep macOS awake while an assistant turn is running:

```sh
tau --caffeinated
```

tau uses `caffeinate -i` and only holds the sleep assertion during active assistant turns. it does not keep the display awake, and it does not apply to `tau rpc` mode. on Linux, `--caffeinated` is accepted but currently a no-op.

## personas

tau comes with several built-in personas across different models:

- **Claude Opus 4.6** (Anthropic): `opus-4.6-chat`, `opus-4.6-coder`
- **Claude Opus 4.8** (Anthropic): `opus-4.8-chat`, `opus-4.8-coder`
- **GPT-5.3-Codex** (OpenAI): `gpt-5.3-codex`
- **GPT-5.4** (OpenAI): `gpt-5.4-chat`, `gpt-5.4-coder`
- **GPT-5.3-Codex (ChatGPT)** (OpenAI Codex): `gpt-5.3-codex-chatgpt`
- **GPT-5.4 (ChatGPT)** (OpenAI Codex): `gpt-5.4-chatgpt-chat`, `gpt-5.4-chatgpt-coder`
- **GPT-5.3-Codex Fast (ChatGPT)**, **GPT-5.4 Fast (ChatGPT)**, and **GPT-5.5 Fast (ChatGPT)** (OpenAI Codex, priority tier): `gpt-5.3-codex-fast-chatgpt`, `gpt-5.4-chatgpt-fast-chat`, `gpt-5.4-chatgpt-fast-coder`, `gpt-5.5-chatgpt-fast-chat`, `gpt-5.5-chatgpt-fast-coder`
- **GPT-5.5** (OpenAI): `gpt-5.5-chat`, `gpt-5.5-coder`
- **GPT-5.5 (ChatGPT)** (OpenAI Codex): `gpt-5.5-chatgpt-chat`, `gpt-5.5-chatgpt-coder`
- **Gemini 3.1 Pro** and **Gemini 3 Flash** (Google): `gemini-3.1-pro-chat`, `gemini-3-flash-chat`

chat variants are for general-purpose assistance; coder variants are optimized for software engineering. built-in personas include the `default` sub-agent for background tasks unless disabled.

switch personas at startup with `--persona` or mid-session with `/persona:<id>`:

persona id matching is exact/case-sensitive.

```sh
tau --persona opus-4.8-coder
```

## sub-agents

some personas can run isolated sub-agents via the `spawn_agent`, `send_input_to_agent`, `wait_for_agent`, and `terminate_agent` tools. sub-agents report progress in the subagent panel, and `wait_for_agent` returns their final output when they finish.

the built-in `default` sub-agent is available unless disabled. it inherits the main persona's model, settings, tool access (minus sub-agent management tools), risk level, and system prompt. the inherited main prompt is wrapped with default sub-agent-specific rules, and those wrapper rules take precedence on conflicts. custom sub-agents can override model, reasoning, tools, and risk level. a sub-agent configured with `riskLevel: read-write` can perform writes even when the main session is `read-only`.

`spawn_agent` supports an optional launch override string (`model: "<provider>/<model>:<effort>"`) and an optional `workingDirectory`. when `workingDirectory` is set, the sub-agent runs from that directory and its prompt context (cwd, AGENTS.md scope, and skills block) is rebuilt as if tau was started there. launch overrides are allowlisted per subagent. custom subagents can define `launchModels` in persona frontmatter, and the built-in `default` sub-agent uses `subagents.defaultLaunchModels` from config.

sub-agent progress appears in a sticky panel. use `alt+down` to cycle active subagents and `ctrl+g` to terminate the selected one. tau caps active subagents at 8.

to use `web_search`/`web_fetch` in a sub-agent, set `apiKeys.parallel` in `~/.config/tau/config.json` (see above) or export `PARALLEL_API_KEY`. tau will only make web calls when you explicitly ask for web research.

## trigger sensitivity

sub-agents and skills define when they should be activated via trigger sensitivity levels:

- **eager**: use proactively whenever the capability would help, even if not explicitly requested. example: a dedicated codebase investigation sub-agent.
- **balanced**: use when the request clearly matches the capability. this is the default if not specified. good for skills that solve specific problems but shouldn't be assumed.
- **explicit**: use only when the user specifically names or requests it. example: a web research sub-agent that should only run when asked.

when you write custom skills, you can specify trigger sensitivity in the skill description. if not specified, the default is balanced. the model respects these levels and won't trigger a skill or sub-agent inappropriately.

## reasoning

some models support extended thinking, where they reason through problems before responding. cycle through reasoning levels with `shift+tab`, or set one at startup:

```sh
tau --persona opus-4.8-chat:high
```

toggle visibility of the model's thinking with `ctrl+t`.

## working with files

reference files in your message with `@<path>` (for example, `@src/tui/app.ts`). autocomplete helps you find the right path. press `ctrl+f` to expand file contents into the conversation, letting the model see the actual code.

reference skills with `@@skill:<name>` (for example, `@@skill:skill-name`). autocomplete will suggest available skills. press `ctrl+f` to expand the skill's `SKILL.md` into the conversation.

to explicitly target a sub-agent, use `@@agent:<name>` (for example, `@@agent:default`).

you can also pipe content directly:

```sh
cat src/tui/app.ts | tau --persona opus-4.8-chat
```

by default, tau injects your AGENTS.md into the system prompt. use `--no-agent-context-files` to disable this behavior. tau searches for AGENTS.md in the current directory and parent directories up to your home folder (or filesystem root if cwd is outside home). tau also includes a paths-only listing of `AGENTS.md` files in child directories under the current working directory, excluding any file already injected in full.

you can also include additional `AGENTS.md` files via config (when that config is in scope for the current working directory):

```json
{ "agentContextFiles": ["packages/pkg1/AGENTS.md"] }
```

paths are resolved relative to the directory containing `.tau/` (or relative to home for the global config when it is in scope). entries are only included when their directory is an ancestor or descendant of the current working directory (sibling paths are ignored).

run `tau --help` to see all available options, or `tau --debug` to inspect loaded personas, prompts, skills, and the full system prompt for debugging configuration issues.

## memory mode

prefix a single-line message with `#` to update AGENTS.md. this is useful for capturing decisions, conventions, and context as you work.

```
# prefer explicit error messages with context about what operation failed
```

tau updates the nearest `AGENTS.md` in your current directory ancestry (or creates one in the current directory if none exists). it integrates the new information into the existing structure. this file is loaded automatically in future sessions unless you pass `--no-agent-context-files`.

## commands

tau supports slash commands for common actions:

| command | description |
| --- | --- |
| `/help` | show available commands |
| `/new` | clear the session and start fresh |
| `/rewind` | open a picker to rewind context from a selected user message |
| `/copy:text` | copy the last assistant message |
| `/copy:code` | copy just the code blocks |
| `/checkpoint` | save a checkpoint file for loading later |
| `/reload` | reload personas, model overrides, prompts, skills, themes, bash commands, and AGENTS.md |
| `/listen` | start microphone recording and transcribe into the editor (macOS only) |
| `/speak` | speak the last assistant message aloud (macOS only) |
| `/cd` | change the working directory |
| `/diff [git diff args...]` | open the diff review tool for a captured review snapshot: plain `/diff` uses the current working tree, while `/diff ...` uses the requested `git diff` args (built-in browser demo by default, `diffTool` overrides it) |
| `/compact:summary-only` | compress history into one synthetic user summary message |
| `/compact:summary-and-last` | compress history and include the last assistant message verbatim when present |
| `/prune:earliest` | prune bash tool results from oldest to newest and compact edit payloads/results |
| `/prune:largest` | prune largest bash tool results first and compact edit payloads/results |
| `/prune:smart` | prune bash tool results via model selection and compact edit payloads/results |
| `/persona:<id>` | switch to a different persona |
| `/prompt:<id>` | insert a saved prompt template |
| `/theme:<id>` | switch to a loaded theme |
| `/bash:<id>` | run a saved shell command |
| `/risk:read-only` | allow read-only tool calls |
| `/risk:read-write` | allow all tools |
| `!<cmd>` | run a shell command directly (bypasses risk checks) |
| `!!<cmd>` | run a shell command without adding output to the model context |

use `tau -l <file>` to resume from a checkpoint created by `/checkpoint`.

tau automatically compacts long sessions when provider-reported usage approaches the model context limit. automatic compaction summarizes older context, retains a recent tail verbatim, and inserts a hidden continuation note so the assistant continues without asking you to repeat context.

the compact commands are manual and useful when you want to force a reset. they replace prior context with a single synthetic user summary message and do not retain a recent tail. `/compact:summary-and-last` also includes the last assistant message verbatim when present.

the prune commands drop bash tool results from the active context without summarizing and compact edit call payloads/results. all three accept an optional fraction between `0` and `1` (for example, `/prune:largest 0.4`) and default to `0.25` when omitted. `/prune:smart` also accepts optional guidance text, either after a fraction (for example, `/prune:smart 0.3 keep only repetitive output`) or by itself (for example, `/prune:smart keep build logs`).

`/listen` (or `ctrl+y`) starts microphone recording on macOS. while recording, editor typing is disabled, and `ctrl+y` stops recording and starts transcription at the cursor. recording also auto-stops after 5 minutes. on Linux, `/listen` is currently unavailable and tau shows a warning.

`/speak` rewrites the last assistant message into naturally speakable text with Gemini 3.5 Flash, synthesizes audio with Gemini 3.1 Flash TTS, and starts playing on macOS at 1.4x speed as soon as the first speech chunk is ready.

`/rewind` opens a picker over prior user messages in the current context. it truncates history from the selected message onward (including the selected message) and prefills the editor with that message so you can retry from there.

`/diff` only starts when tau is idle. it captures the requested `git diff` output at launch time as the initial review context, opens tau's built-in browser diff review demo when `diffTool` is not configured, and lets `diffTool` override that launcher when it is configured. the built-in browser shows that captured diff, but review agents inspect the live repo state while using the captured diff context as their starting point. tau shows review status in the chat stream, keeps the editor usable for drafting, but blocks normal submission until the tool returns review text or cancels. returned review text is appended as a review-styled user message without auto-running the assistant, and the model-visible message is wrapped in a hidden `<system>` block that identifies it as diff review feedback for that review context. if the tool never connects or disconnects before returning a result, tau cancels the review and unblocks the session. press `esc` to cancel locally.

the main assistant also has a TUI-only `diff_review` tool. it uses the same captured review session and live status UI as `/diff`, but it is only for cases where you explicitly ask the agent to start a diff review. when the review returns, the feedback is delivered as a normal tool result so the assistant continues in the same turn; it is not inserted as a separate hidden-system user message.

## keyboard shortcuts

| key         | action                                     |
| ----------- | ------------------------------------------ |
| `shift+tab` | cycle reasoning effort                     |
| `ctrl+r`    | cycle risk level                           |
| `ctrl+p`    | cycle personality                          |
| `ctrl+t`    | toggle thinking visibility                 |
| `ctrl+o`    | toggle compact tool display                |
| `ctrl+f`    | expand @<file> and @@skill:<name> mentions |
| `ctrl+s`    | stash input to clipboard                   |
| `ctrl+y`    | toggle voice recording (`/listen`)         |
| `ctrl+g`    | terminate selected sub-agent               |
| `enter x2`  | retry last response on empty input         |
| `esc x2`    | clear current prompt                       |
| `alt+up`    | pop queued message                         |
| `alt+down`  | cycle active sub-agents                    |
| `esc`       | interrupt active task or cancel `/diff`    |
| `ctrl+c`    | press twice to exit                        |

## configuration

### global config

tau loads config from `~/.config/tau/config.json` only when the current working directory is inside your home directory. it also loads any `.tau/config.json` found by walking up from the current working directory to home (or to the filesystem root when cwd is outside home). settings merge from least-specific to most-specific.

model definitions can be extended and overridden through `~/.config/tau/models.json` and `.tau/models.json` with the same discovery and precedence rules as `config.json`. see [docs/models.md](docs/models.md).

```json
{
  "apiKeys": {
    "anthropic": "sk-ant-...",
    "openai": "sk-...",
    "google": "...",
    "parallel": "...",
    "mistral": "..."
  },
  "defaultPersona": "gpt-5.4-chat",
  "defaultRisk": "read-write",
  "disableBuiltinPersonas": false,
  "disableBuiltinThemes": false,
  "defaultTheme": "solarized",
  "diffTool": {
    "command": "./scripts/my-diff-tool",
    "args": ["--browser"],
    "env": { "TAU_DIFF_UI": "browser" }
  },
  "subagents": {
    "defaultLaunchModels": [
      "openai/gpt-5.4:high",
      "anthropic/claude-haiku-4-5:low"
    ]
  },
  "autoCompact": {
    "enabled": true,
    "reserveTokens": 16384,
    "keepRecentTokens": 20000
  },
  "modelSystemNotices": {
    "openai-codex/gpt-5.3-codex": "avoid apply_patch heredocs, use tau tools directly"
  }
}
```

for built-in providers and features, the `apiKeys` field uses these keys: `anthropic`, `openai`, `google`, `parallel`, and `mistral`. keys are merged across config levels by key name.

the `defaultPersona` field specifies which persona to use when starting the app. it accepts `<id>` or `<id>:<reasoning>`, and matching is exact/case-sensitive. the `--persona` flag overrides this setting.

the `defaultRisk` field sets the initial risk level (`read-only` or `read-write`). the `--risk` flag overrides this setting. if not specified, defaults to `read-only`.

the `defaultTheme` field sets the theme id to load at startup. it must be non-empty, and matching is exact/case-sensitive. if not specified, it defaults to `gold`.

tau ships a built-in browser diff review demo tool, so `/diff` works without any `diffTool` config. set `diffTool` only when you want to override that default launcher. `command` is required when `diffTool` is present. `args` and `env` are optional. relative `command` paths resolve from the config level root (directory containing `.tau`, or home for the global config). set `builtInDiffTool.codeTheme` to choose the built-in diff tool's initial code theme, for example `{ "builtInDiffTool": { "codeTheme": "github-dark-dimmed" } }`. the default is `github-dark-dimmed`.

supported built-in diff tool code themes are: `andromeeda`, `aurora-x`, `ayu-dark`, `ayu-mirage`, `catppuccin-frappe`, `catppuccin-macchiato`, `catppuccin-mocha`, `dark-plus`, `dracula`, `dracula-soft`, `everforest-dark`, `github-dark`, `github-dark-default`, `github-dark-dimmed`, `github-dark-high-contrast`, `gruvbox-dark-hard`, `gruvbox-dark-medium`, `gruvbox-dark-soft`, `horizon`, `horizon-bright`, `houston`, `kanagawa-dragon`, `kanagawa-wave`, `laserwave`, `material-theme`, `material-theme-darker`, `material-theme-ocean`, `material-theme-palenight`, `min-dark`, `monokai`, `night-owl`, `nord`, `one-dark-pro`, `plastic`, `poimandres`, `red`, `rose-pine`, `rose-pine-moon`, `slack-dark`, `solarized-dark`, `synthwave-84`, `tokyo-night`, `vesper`, `vitesse-black`, `vitesse-dark`.

the `subagents.defaultLaunchModels` field configures allowed `spawn_agent` launch overrides for the built-in `default` sub-agent. values must use `<provider>/<model>:<effort>`.

`autoCompact` controls automatic session compaction and merges field-by-field across config levels. it is enabled by default with `reserveTokens: 16384` and `keepRecentTokens: 20000`. tau triggers it only after provider-reported assistant usage crosses the model context window minus the reserve, then summarizes older context while retaining recent messages verbatim (capped at that threshold). manual `/compact:*` commands remain summary-reset commands.

the `modelSystemNotices` field maps `<provider>/<model>` to a notice string. provider ids must be known and model ids are exact/case-sensitive against the merged configured model catalog (built-in + layered `models.json`). when a message is sent to that model, tau prepends the notice as a `<system>...</system>` block before the user content. this applies to main-session user messages and sub-agent prompts, regardless of persona id.

if `disableBuiltinPersonas` is set to `true`, tau will not load built-in personas. if `disableBuiltinThemes` is set to `true`, tau will not load built-in themes. only entries from `~/.config/tau/` and `.tau/` will be available for those categories. you can also set these flags in any `.tau/config.json`; the most specific value wins.

the `async` field in normal tau config is client-side only:

- `async.client.defaultTarget` + `async.client.targets`: client-side URL/token target definitions for `tau async ...` commands.
- `async.client.defaultProjectId`: default project id used by `tau async <prompt...>` when `--project` is omitted.

example (`~/.config/tau/config.json` or `.tau/config.json`):

```json
{
  "async": {
    "client": {
      "defaultTarget": "local",
      "defaultProjectId": "tau",
      "targets": {
        "local": {
          "url": "http://127.0.0.1:7788",
          "token": "replace-me"
        }
      }
    }
  }
}
```

daemon-side async settings are in a separate config file passed to:

```sh
tau async daemon --config-file <path>
```

see [docs/async.md](docs/async.md) for daemon config schema (`host`, `port`, `authToken`, `telegram` (map keyed by bot id), `cron` (including `cron.jobsDir`), `projects`, `workspaceRoot`, `projects.<id>.ref`, `projects.<id>.workingDirectory`, `projects.<id>.description`, `projects.<id>.bootstrapCommands`, `projects.<id>.backgroundBootstrapCommands`) and GitHub repo requirements (`owner/repo`, cloned via `gh repo clone`).

### project bash commands

define shortcuts for common shell commands in any in-scope config file (`~/.config/tau/config.json` when cwd is under home, or `.tau/config.json` in the cwd ancestry). entries merge by `id` with the most specific level winning:

```json
{
  "bashCommands": [
    {
      "id": "check",
      "description": "lint + typecheck",
      "cmd": "npm run check"
    },
    {
      "id": "test",
      "cmd": "npm test"
    }
  ]
}
```

run them with `/bash:check` or `/bash:test`.

commands run with cwd set to the config level root (directory containing `.tau`, or home for the global config).

### diff review tool

tau ships `tau diff-tool`, a built-in browser diff review demo tool. `/diff` launches it by default when `diffTool` is not configured. configure `builtInDiffTool.codeTheme` to choose the built-in tool's initial code theme; the default is `github-dark-dimmed`.

if you want a different launcher, configure `diffTool` in any in-scope config file. when present, it overrides the built-in fallback:

```json
{
  "diffTool": {
    "command": "./scripts/my-diff-tool",
    "args": ["--browser"],
    "env": { "TAU_DIFF_UI": "browser" }
  }
}
```

`tau diff-tool --help` shows the built-in demo tool's standalone help text.

plain `/diff` captures the current working-tree review scope before launch, including tracked staged + unstaged changes plus untracked text files that fit within tau's snapshot limits. `/diff [git diff args...]` with arguments passes those raw arguments to `git diff`, so `/diff --staged` and `/diff -- src/foo.ts` still work. tau shows diff-review status in the chat stream, keeps the editor usable while blocking submission, and appends returned review text as a review-styled user message without auto-running the assistant. the built-in browser shows that captured review snapshot, but review agents inspect the live repo state while using the captured snapshot as their starting point. the model-visible message is wrapped in a hidden `<system>` block that identifies it as diff review feedback for that review context. if the tool never connects or disconnects before returning a result, tau cancels the review and unblocks the session. during normal shutdown, tau now asks the diff tool to exit via the diff-review protocol before closing the transport. custom diff tools should follow the built-in tool and treat that explicit shutdown request as the canonical way to stop.

in the TUI, the main assistant can also call the `diff_review` tool when you explicitly ask it to start a diff review. the tool can capture structured `git diff` args or one or more prebuilt patch files for selected-hunk reviews, shows the same live session status in a normal tool card, and returns review feedback to the model as a normal tool result so the assistant can continue immediately.

### additional agents context

you can tell tau to always include extra `AGENTS.md` files by adding an `agentContextFiles` list to a config file in scope:

```json
{ "agentContextFiles": ["packages/pkg1/AGENTS.md"] }
```

paths are resolved relative to the directory containing `.tau/` (or relative to home for the global config when it is in scope). entries must point at `AGENTS.md`. entries are only included when their directory is an ancestor or descendant of the current working directory (sibling paths are ignored). child `AGENTS.md` files that are not injected in full are still listed by path in the project context.

### custom personas

create your own personas by adding markdown files to `~/.config/tau/personas/` (global, only when cwd is under home) or `.tau/personas/` (project). `.tau/` directories are discovered by walking up from the current working directory to home (or filesystem root if cwd is outside home):

```markdown
---
id: my-assistant
provider: anthropic
model: claude-opus-4-8
---

you are a helpful assistant specialized in my workflow. focus on clarity and efficiency.
```

the frontmatter defines the persona. required fields:

- `id`: unique id used by `--persona` and `/persona:<id>`
- `provider`: model provider id (for example `openai`, `anthropic`, `google`)
- `model`: model id for the provider (for example `gpt-5.4`, `claude-opus-4-8`)

custom personas/subagents can reference model ids that are not bundled yet, as long as the provider is known. built-in personas use the merged model catalog, so `models.json` can override bundled model definitions. see [docs/models.md](docs/models.md).

the persona file name (without the `.md` extension) must match the `id`.

optional frontmatter fields:

- `label`: display name shown in the ui (defaults to the base persona label if `extends` is used)
- `description`: human-readable description used in lists/autocomplete
- `extends`: inherit optional fields from a built-in persona id (for example `gpt-5.4-coder`). `provider` and `model` are still required. if the markdown body is empty, the base persona's system prompt is used.
- `reasoning`: one of `none`, `minimal`, `low`, `medium`, `high`, `xhigh`
- `serviceTier`: `priority` or `flex` for providers that support service tiers (currently `openai` and `openai-codex`)
- `allowedReasoningLevels`: list of reasoning levels shown in the ui
- `skills`: list of enabled skill names (matched by `name` in skill frontmatter), or `"*"` to enable all discovered skills. if omitted, custom personas default to `"*"`. set `skills: []` to disable skills completely.
- `subagents`: optional map of subagent definitions. the built-in `default` sub-agent is implicit unless `default: false` is provided. custom subagents must include `systemPrompt` and may include `description`, `provider`+`model`, `reasoning`, `serviceTier`, `tools`, `riskLevel`, and `launchModels` (when specifying a model, `provider` and `model` must be provided together). names must be lowercase with dashes (max 64 chars). `launchModels` entries must use `<provider>/<model>:<effort>` and are used to allowlist launch-time `spawn_agent` overrides. example:
  ```yaml
  subagents:
    default: false
    web-research:
      systemPrompt: |
        you are a focused web research sub-agent.
      description: web research using web_search/web_fetch.
      provider: anthropic
      model: claude-haiku-4-5
      reasoning: medium
      tools: [web_search, web_fetch, bash]
      riskLevel: read-only
      launchModels:
        - openai/gpt-5.4:high
        - anthropic/claude-haiku-4-5:medium
  ```
- `tools`: list of tool names to enable for this persona. allowed: `bash`, `write`, `edit`, `view_image`, `diff_review`, `spawn_agent`, `send_input_to_agent`, `wait_for_agent`, `terminate_agent`. if omitted, defaults to `bash`, `write`, `edit`, `view_image`, `diff_review` (and subagent tools when subagents are enabled). risk levels still apply.

the markdown body becomes the system prompt.

use it with `--persona my-assistant` or `/persona:my-assistant`. if a project persona id conflicts with a user or built-in persona, the project persona wins.

to clone a built-in persona but swap the provider/model, use `extends`:

```markdown
---
id: my-haiku-coder
extends: gpt-5.4-coder
provider: anthropic
model: claude-haiku-4-5
---
```

when persona ids collide across levels, the most specific level wins (for example, a `.tau/personas/` entry overrides a global or built-in persona).

### custom prompts

tau does not include prompt templates by default. run `tau install` to bootstrap starter templates, or save your own in `~/.config/tau/prompts/` (global, only when cwd is under home) or `.tau/prompts/` (project). `.tau/` directories are discovered by walking up from the current working directory to home (or filesystem root if cwd is outside home):

```markdown
---
id: review
---

review this code for bugs, edge cases, and style issues. suggest specific improvements with code examples.
```

insert them with `/prompt:review`. if a prompt id conflicts across levels, the most specific level wins.

the prompt file name (without the `.md` extension) must match the `id`.

### skills

skills are optional directories discovered at `~/.config/tau/skills/` and `~/.agents/skills/` (global, only when cwd is under home), plus `.tau/skills/` and `.agents/skills/` in the cwd ancestry (up to home, or filesystem root if cwd is outside home). each skill is a directory containing `SKILL.md`. tau follows the [agent skills spec](https://agentskills.io/home). when `.tau/skills/` and `.agents/skills/` both exist at the same level, `.agents/skills/` wins on name conflicts.

`SKILL.md` must start with yaml frontmatter:

- `name`: 1-64 chars, `a-z0-9-`, must match the directory name
- `description`: 1-1024 chars

optional fields: `license`, `compatibility` (<=500 chars), `metadata` (string map), `allowed-tools` (validated, currently ignored by tau).

enable skills per persona with the `skills` frontmatter field. you can list specific skill names (matched by `name` in skill frontmatter), use `"*"` to enable all discovered skills, or set `skills: []` to disable skills completely. built-in personas and custom personas with omitted `skills` default to `skills: "*"`. if a project skill conflicts with a user skill by name, the project skill wins. tau injects an index of enabled skills into the system prompt containing only each skill's `name`, `description`, and file path.

use `/reload` to pick up changes to personas, model overrides, prompts, skills, themes, bash commands, and AGENTS.md without restarting.

## how it works

tau connects your terminal to large language models, giving them tools to interact with your filesystem. when you ask the model to explore code or make changes, it decides which tools to use and executes them subject to the active risk level.

the model sees your messages, any file contents you've shared, and the results of tool calls. it doesn't have ambient access to your filesystem; it only sees what you show it or what it explicitly requests through tools.

tool calls are displayed in the UI so you can see exactly what the model is doing. use `ctrl+o` to toggle between compact and detailed views.

## tool output truncation

tool output is truncated using a `bytes / 6` token heuristic (shown as `…N tokens truncated…`).

- **bash (assistant)**: 8,192 token limit. if output exceeds this and `maxOutputTokens` is unset, output is middle-truncated to a 2,048-token gated preview. re-run with `maxOutputTokens` set to 8,192-16,384; if the user explicitly requests more, it may be set up to 65,536 (user requests are checked). bash captures the last 1MB of output.
- **bash (user `!`)**: 65,536 token limit.
- **web_search/web_fetch**: large responses are middle-truncated to their token limits (8,192 / 16,384 tokens).

## creating a release

publishing to npm happens automatically via GitHub Actions when a GitHub release is published.

release steps:

- install dependencies for the root package and the built-in diff tool app:

```sh
npm ci
(cd src/diff_tool/app && npm ci)
```

- run checks and build:

```sh
npm run check
npm run build
npm test
```

- bump the version (creates a git tag):

```sh
npm version patch
```

- push the commit and tag:

```sh
git push --follow-tags
```

- create a GitHub release (this triggers the publish workflow):

```sh
gh release create v$(node -p "require('./package.json').version") --generate-notes
```

alpha prereleases are published under the npm `alpha` tag (not `latest`):

```sh
if node -p "require('./package.json').version.includes('-alpha.')"; then
  npm version prerelease --preid alpha
else
  npm version preminor --preid alpha
fi
gh release create v$(node -p "require('./package.json').version") --generate-notes --prerelease
```
